Criteria for use of PSV / TSV???

[Guibar]

Hello all,

I am looking for any guide or standard that defines when do we need to use a PSV or TSV in pipelines or even in short distance pipes. In all HAZOP I participate, people always ask if should or should not have a safety valve in a pipe (any pipe). The answer I always hear is " it is a project designer definition or it is a designer criteria".
Could someone help me?

Thanks

 

[e43u8]

GUIBAR,

As general rules for PSV/TSV requirements in piping systems:

-No PSV is required for process upset cases
-PSV for fire case is required if piping can be isolated and can be exposed to fire; also the weight of the trapped fluid including flammable gas/liquified HC/liquid HC is higher than 2-3 tons
-TSV for thermal expansion may be required if piping contains liquid especially liquified HC/liquid HC can be isolated and/or can be exposed to external heat such as sun shine

 

[Guibar]

e443u,

thank you for your answer.

Although, would you know any standard that refers to those items you have listed or are they engineering good practices?

 

[LittleInch]

In the most basic terms, the first page of ASME B £1.3 Chapter II Design contains the following section below.

What you generally find, due to the absolute temperature being used for gas expansion is that pipe either wholly or partly gas filled, does not normally require TRVs due to solar heating.

However liquid filled lines, especially HC, can achieve very high pressures via solar heating (3-4 bar per degree C is not uncommon).

Liquid manifolds can end up with a lot of TRVs if you're not careful. Locking iopen certain valves can work, but adds a lot to the operation and TRVs are normally quite cheap.

I don't agree with the statement that PSVs are not required for process upset - depends on how much that "process upset" is.

301.2.2 Required Pressure Containment or Relief
(a) Provision shall be made to safely contain or relieve
(see para. 322.6.3) any expected pressure to which the
piping may be subjected. Piping not protected by a pressure
relieving device, or that can be isolated from a
pressure relieving device, shall be designed for at least
the highest pressure that can be developed.
(b) Sources of pressure to be considered include ambient
influences, pressure oscillations and surges,
improper operation, decomposition of unstable fluids,
static head, and failure of control devices.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Duwe6]

"I don't agree with the statement that PSVs are not required for process upset - depends on how much that "process upset" is."

Exactly; if there is the slightest chance of a decomposition reaction, you need a nice, big rupture disk pointing somewhere safe. Beats launching a few lengths of pipe into the process unit.

 

[e43u8]

LittleInch,

Of course, to state lack of requirement to PSV due to process upset I did assume, as normally is, piping is protected against the maximum possible pressure under upset conditions (full pressure rated design or PSV installed upstream of it). Otherwise a process PSV is required.

 

[CMA010]

The "relief Systems Handbook" of Parry gives criteria for thermal relief. Furthermore there are some articles that give guidance ("What you should know about liquid thermal expansion", HP November 2008, and "Decide whether to use thermal relief valves", CEP December 1993).